Giga-tronics 8650A Series, Operation Manual

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Series 8650A Universal Power Meters
2-30 Manual 31470, Rev. E, April 2001
Peak power measurements are made by sampling the RF input at a point which is defined by a trigger
level, a delay, and a delay offset (see Figure 2-17). The initial triggering event occurs when the power
input (or in the case of external triggering, a voltage input) reaches a threshold, which you have defined
as the trigger level. The sample is then taken after a delay, which you have defined. To this delay can be
added a positive or negative delay offset.
The delay offset is not necessary for peak measurement, but in some applications it is a convenience. For
example, a small offset (even a negative offset) might compensate for the difference between the trigger
point and some other point of interest (such as the half-power point) especially in applications where
pulse width is being measured. Or if it is necessary to measure the levels of various pulses within a pulse
train, the pulses can be sampled successively by changing the delay offset. A fixed delay insures that
each pulse is sampled at the same point in its cycle.
Figure 2-17: Delay and Delay Offsets
Peak Power, Sampled After a 120 ns Delay
Sample Sample
120 ns
Delay
120 ns
Delay
Trigger
Point Trigger
Point
Time
Time (Microseconds)
Time
Trigger
Level
Trigger
Level
Po
w
e
r
Po
w
e
r
Po
w
e
r
10 ns
Delay
Offset
Half-Power
Point
Peak Power, Sampled After a 120 ns Delay
and a 10 ns Delay Offset
Peak Power, Sampled With a Fixed Delay
But Various Delay Offsets
Trigger
Sample
(No Offset)
Delay Offset
Delay Offset
Sample
(11
µ
s Offset)
Sample
(22
2.8
µ
s
Offset
0 2 4 6 8 10 12 14 16 18 20 22
24
26 28 30
32
µ
s Offset)